[CentOS] RAID 6 - opinions

[Seth Bardash]

We build a storage unit that anyone using Centos can build. It is based on the 3ware 9750-16 controller. It has 16 x 2 TB Sata 6 gb/s disks. We always set it up as a 15 disk RAID 6 array and a hot spare. We have seen multiple instances were the A/C has gone off but the customer's UPS kept the systems running for an hour or two with no cooling. Once the ambient temperature goes above 40C you are stressing all the disks in the array. I ramble about this BECAUSE we have seen many RAID 5 arrays fail while rebuilding with a hot spare and then loose all the data. 

The chances of this happening on a R6 array are much much lower. 
Now for performance numbers: 550 MB/SEC on writes and 1150 MB/SEC on reads.
 
A unit like this can support any type of I/O you want to put into it as Centos will usually either have thedrivers built in or you can add then easily.

Also the rebuild time for a 50 TB array is about 12 hours while the array is in use and online. But during this time there is little or no degradation in performance.

The down side is the cost of the controller. If anyone has questions about this I would be glad to answer them off line : at seth at integratedsolutions dot org.




Adrian Sevcenco <Adrian.Sevcenco at cern.ch> wrote:

>On 04/11/2013 06:36 PM, m.roth at 5-cent.us wrote:
>> I'm setting up this huge RAID 6 box. I've always thought of hot spares,
>> but I'm reading things that are comparing RAID 5 with a hot spare to RAID
>> 6, implying that the latter doesn't need one. I *certainly* have enough
>> drives to spare in this RAID box: 42 of 'em, so two questions: should I
>we use several of this kind of boxes (but with 45 trays) and our
>experience was that the optimum volume size was 12 hdds (3 X 12 + 9)
>which will reduce the 45 disks to a actual size of 37 disks (a 12 disk
>volume is 40 TB size ... in event of a broken hdd it takes 1 day to
>recover.. more than 12 disks and i dont (want to) know how long it would
>take) and we don't use hot spares.
>
>HTH,
>Adrian
>
>
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